Search Results (274)

Graphene quantum dots (GQDs) obtained by microwave-induced pyrolysis of glutamic acid and triethylenetetramine (trien) are fairly stable, emissive, water-soluble, and positively charged nano-systems able to interact with negatively charged meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS₄). The stoichiometric control during the preparation affords a supramolecular adduct, GQDs@TPPS₄, that exhibits a double fluorescence emission from both the GQDs and the TPPS₄ fluorophores. These supramolecular aggregates have an overall negative charge that is responsible for the condensation of cations in the nearby aqueous layer, and a three-fold acceleration of the metalation rates of Cu²⁺ ions has been observed with respect to the parent porphyrin. Addition of various metal ions leads to some changes in the UV/Vis spectra and has a different impact on the fluorescence emission of GQDs and TPPS₄. The quenching efficiency of the TPPS₄ emission follows the order Cu²⁺ > Hg²⁺ > Cd²⁺ > Pb²⁺ ~ Zn²⁺ ~ Co²⁺ ~ Ni²⁺ > Mn²⁺ ~ Cr³⁺ >> Mg²⁺ ~ Ca²⁺ ~ Ba²⁺, and it has been related to literature data and to the sitting-atop mechanism that large transition metal ions (e.g., Hg²⁺ and Cd²⁺) exhibit in their interaction with the macrocyclic nitrogen atoms of the porphyrin, inducing distortion and accelerating the insertion of smaller metal ions, such as Zn²⁺. For the most relevant metal ions, emission quenching of the porphyrin evidences a linear behavior in the micromolar range, with the emission of the GQDs being moderately affected through a filter effect. Deliberate pollution of the samples with Zn²⁺ reveals the ability of the GQDs@TPPS₄ adduct to detect sensitively Cu²⁺, Hg^2+, and Cd²⁺ ions. Full article

Chromium slag sites pose severe environmental risks due to hexavalent chromium (Cr(VI)) contamination, characterized by high mobility and toxicity. This study focused on chromium-contaminated soil from a historical chromium slag site in North China, where long-term accumulation of chromate production residues has led to serious Cr(VI) pollution, with Cr(VI) accounting for 13–22% of total chromium and far exceeding national soil risk control standards. To elucidate Cr(VI) transformation mechanisms and elemental linkages, a combined approach of macro-scale condition experiments and micro-scale analysis was employed. Results showed that acidic conditions (pH < 7) significantly enhanced Cr(VI) reduction efficiency by promoting the conversion of CrO₄²⁻ to HCrO₄⁻/Cr₂O₇²⁻. Among reducing agents, FeSO₄ exhibited the strongest effect (reduction efficiency >30%), followed by citric acid and fulvic acid. Temperature variations (−20 °C to 30 °C) had minimal impact on Cr(VI) transformation in the 45-day experiment, while soil moisture (20–25%) indirectly facilitated Cr(VI) reduction by enhancing the reduction of agent diffusion and microbial activity, though its effect was weaker than chemical interventions. Soil grain-size composition influenced Cr(VI) distribution unevenly: larger particles (>0.2 mm) in BC-35 and BC-36-4 acted as main Cr(VI) reservoirs due to accumulated Fe-Mn oxides, whereas BC-36-3 showed increased Cr(VI) in smaller particles (<0.074 mm). μ-XRF and correlation analysis revealed strong positive correlations between Cr and Ca, Fe, Mn, Ni (Pearson coefficient > 0.7, p < 0.01), attributed to adsorption–reduction coupling on iron-manganese oxide surfaces. In contrast, Cr showed weak correlations with Mg, Al, Si, and K. This study clarifies the complex factors governing Cr(VI) behavior in chromium slag soils, providing a scientific basis for remediation strategies such as pH adjustment (4–6) combined with FeSO₄ addition to enhance Cr(VI) reduction efficiency. Full article

Municipal solid waste (MSW) and refuse-derived fuel (RDF) incineration generate over 20 million tons of residues annually in the EU. These include bottom ash (IBA), fly ash (FA), and air pollution control residues (APCr), which pose significant environmental challenges due to their leaching potential and hazardous properties. While these residues contain valuable metals and reactive mineral phases suitable for carbonation or alkaline activation, chemical, techno-economic, and policy barriers have hindered the implementation of sustainable, full-scale management solutions. Accelerated carbonation technology (ACT) offers a promising approach to simultaneously sequester CO₂ and enhance residue stability. This review provides a comprehensive assessment of waste incineration residue carbonation, covering 227 documents ranging from laboratory studies to field applications. The analysis examines reactor designs and process layouts, with a detailed classification based on material characteristics, operating conditions, investigated parameters, and the resulting pollutant stabilization, CO₂ uptake, or product performance. In conclusion, carbonation-based approaches must be seamlessly integrated into broader waste management strategies, including metal recovery and material repurposing. Carbonation should be recognized not only as a CO₂ sequestration process, but also as a binding and stabilization strategy. The most critical barrier remains chemical: the persistent leaching of sulfates, chromium(VI), and antimony(V). We highlight what we refer to as the antimony problem, as this element can become mobilized by up to three orders of magnitude in leachate concentrations. The most pressing research gap hindering industrial deployment is the need to design stabilization approaches specifically tailored to critical anionic species, particularly Sb(V), Cr(VI), and SO₄²⁻. Full article

Freshwater resources are scarce in tropical island areas. Treating rainwater to produce drinking water through biological slow filtration (BSF) technology can significantly alleviate the problem of freshwater shortages. The characteristics of the filter material are the key factors determining the decontamination performance of BSF technology. However, most existing studies focus on a single filter material. This study was conducted using volcanic rock and coconut shell activated carbon to compare their pollutant removal characteristics in slightly polluted rainwater during the early stage of BSF operation (from the start of operation to day 6, with the first sampling time being 48 h after operation) and during the stable stage (26 days later) and further explore the influence of their mixing ratio. The results show that in the early stages of operation, the pollutant removal performance of volcanic rock and coconut shell activated carbon is better than that of quartz sand. Among them, coconut shell activated carbon showed average removal rates for NH₃-N, TOC, and Cr(VI) that were 6.72, 8.46, and 19.01 percentage points higher than those of volcanic rock, respectively, but its average turbidity removal rate decreased by 5.00%. The removal effect of the mixed filter material was enhanced through the synergistic adsorption mechanism, but most of the improvements were within the standard deviation range and did not exceed the removal range of the single filter material. When the mixing ratio was 1:3, the average total organic carbon removal rate of the filter material was 71.51 ± 0.64%, approximately 0.96 percentage points higher than that of coconut shell activated carbon (70.55 ± 0.42%). While coconut shell activated carbon showed the best removal effect among all single filter materials, this improvement was still within the standard deviation range. Full article

Chabazite, a tectosilicate mineral, belongs to the zeolite group and has been widely used for the adsorptive removal of a number of cationic contaminants from the aqueous phase. However, a negatively charged chabazite surface can be altered by chemical modification in order to change its adsorption abilities towards anions. This study reports the potential for the removal of hexavalent chromium ions from aqueous solutions by modified chabazite. In this regard, natural chabazite was modified by the immobilization of HDTMA-Br to achieve double-layer coverage on its surface, defined as the double external cation exchange capacity. Next, a batch adsorption system was applied to study the adsorption of inorganic Cr(VI) anions from aqueous solutions. The process equilibrium was described by 11 theoretical isotherm equations, while 6 adsorption kinetics were represented by four models. Among those tested, the most appropriate model for the description of the studied process kinetics was the pseudo-second order irreversible model. The obtained results suggest that Cr(VI) adsorption takes place according to a complex mechanism comprising both Langmuir-type sorption with the maximum adsorption capacity of modified chabazite, approx. 9.3–9.9 mg g⁻¹, and the trapping of Cr(VI) inside the capillaries of the amorphous sorbent, making it a viable option for water treatment applications. Full article

Microbial remediation of Cr(VI)-polluted wastewater offers an effective and sustainable green method. In this study, a novel strain Priestia megaterium strain BM.1 that was capable of reducing Cr(VI) was domesticated. In order to improve its Cr(VI) reduction and adsorption performance, calcium-modified hydrochar (HC-Ca) was utilized to immobilize the strain to obtain the composite material BM.1-Ca. The BM.1-Ca composite achieved a Cr(VI) removal efficiency of 97% at an initial concentration of 60 mg/L within 60 h, representing a 1.96-fold enhancement compared to BM.1 alone and demonstrating significantly improved microbial Cr(VI) removal capacity. The addition of HC-Ca was instrumental in maintaining the stable Cr(VI) removal efficiency of BM.1 in the presence of altered incubation environments and interference from co-existing ions. The reduction in Cr(VI) by BM.1 and the immobilization of Cr(III) on the surface of BM.1-Ca are the main removal mechanisms of Cr(VI). Analysis of microbial oxidative stress and extracellular polymers showed that HC-Ca was able to attenuate the oxidative stress of BM.1 as well as promote the secretion of extracellular polymers. This study reveals the intrinsic mechanism of the novel material BM.1-Ca for remediation of Cr(VI) pollution in water bodies and provides an effective method for bioremediation of Cr(VI). Full article

Water pollution, driven by industrial wastewater, agricultural runoff, and domestic sewage, introduces organic pollutants (e.g., dyes and antibiotics) and heavy metal ions (e.g., Pb²⁺ and Cr(VI)), threatening ecosystems and human health. Although traditional water treatment technologies have now matured, they still have some deficiencies in terms of specific pollutants. Metal–organic frameworks (MOFs), particularly zeolite imidazole frame-67 (ZIF-67)—a cobalt-based MOF with high surface area, tunable pores, and robust chemical stability—show excellent adsorption capacity for pollutants and have emerged as promising candidates for water treatment due to their efficacy in adsorption, catalysis, and photocatalysis. This review examines ZIF-67’s synthesis, functionalization strategies, and applications in removing organic pollutants and heavy metals. It explores its mechanisms, composite designs, and recyclability, while highlighting challenges and future directions for developing efficient, sustainable water treatment technologies. Full article

While meat consumption trends show decreases in some high-income countries, significant increases are observed elsewhere. Although this includes African nations, the average meat consumption in Africa remains generally lower than in many other continents, though patterns vary regionally. Meat provides essential nutrients, but inadequate consumption can pose health problems, while consumption also carries risks including potential exposure to environmental contaminants. This comprehensive review focuses on the recent scientific literature (published 2000–2024) regarding human exposure to specific toxic trace elements, namely arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), chromium (Cr, particularly hexavalent chromium, Cr(VI)), and nickel (Ni), through the consumption of meat (muscle tissues, organs, and processed products) in Africa. Limited data exist for many African regions, with most studies from Nigeria. Concentrations of these toxic elements in meat tissues varied significantly, with organs like liver and kidney showing higher levels than muscle tissues. Estimated dietary intakes also varied, with some studies indicating potential health risks from Pb, Cd, and As exceeding safety guidelines in specific contexts. However, meat is generally not the primary dietary source of these elements compared to fish, seafood, or staple crops, though risks are higher in areas near pollution sources like mines or waste sites. This study highlights the need for broader research across Central and North Africa, stricter monitoring of meat from high-risk areas, and standardized methodologies to protect public health. Full article

Water pollution by antibiotics and heavy metals threatens the ecological environment and human health globally, yet there is no rapid method to detect multiple antibiotics and metal ions simultaneously. A simple, fast, and ultra-sensitive colorimetric chemosensor for the simultaneous detection of moxifloxacin (MOX), ciprofloxacin (CIP), and Cr(III) based on the aggregation of ammonium thioglycolate (ATG)-functionalized gold nanoparticles (ATG-AuNPs) was developed. Following the addition of MOX, CIP, and Cr(III), a color change in the solution was observed from wine-red to blue-grey. The UV–Vis signal of the ATG-AuNPs system blended with MOX, CIP, and Cr(III) in the range of 0~200 µM, 0~100 µM, and 0~5 µM was assessed and measured with detection limits (LODs) of 1.57 µM, 1.30 µM, and 57.1 nM calculated by 3σ/S, respectively. Therefore, this system has the potential to act as an effective colorimetric chemosensor for simultaneously detecting MOX, CIP, and Cr(III) in complex environmental systems. Full article

Zero-valent iron (ZVI), particularly in its nanoscale form (nZVI), is now considered a highly promising material for the remediation of toxic metal ions from polluted groundwater owing to its strong reductive potential, significant surface area, and reactive behavior. This review systematically explores the application of pristine and modified ZVI systems—including doped ZVI, bio-stabilized composites, and ZVI supported on advanced materials like MXene and nanocellulose—for effective treatment of water containing metal species like As(III/V), Hg(II), Cr(VI), and Ni(II). Emphasis is placed on understanding the underlying mechanisms, including redox reactions, surface complexation, and synergistic adsorption–reduction pathways. Key factors affecting adsorption efficiency—such as pH, temperature, ZVI dosage, and competing ions—are thoroughly analyzed, alongside adsorption kinetics and isotherm models. Modified ZVI composites exhibit enhanced stability, selectivity, and reusability, demonstrating promising performance even in complex aqueous environments. Despite significant progress, challenges such as nanoparticle passivation, limited field-scale data, and potential toxicity of byproducts remain. The review concludes by highlighting future research directions focused on improving material longevity, regeneration efficiency, selective adsorption, and integration with other advanced remediation technologies for sustainable and scalable groundwater treatment. Full article

A polyoxometalate-based metal–organic complex with the ability to treat pollutants in water was obtained under hydrothermal conditions, namely [Ni(H₂L)(HL)₂](PMo₁₂O₄₀)·3H₃O·4H₂O (1) (H₂L = 4,4′-(1H,1′H-[2,2′-biimidazole]-1,1′-diyl)dibenzoicacid). Structural analysis reveals that the [Ni(H₂L)(HL)₂] units are interconnected into a 2D layer via hydrogen bonds between adjacent carboxyl groups and water molecules of crystallization. [PMo₁₂O₄₀]³⁻ anions are embedded within the larger pores of the layer and are connected to the adjacent layers through hydrogen bonds, ultimately expanding the structure into a 3D supramolecular architecture. The intermolecular interactions were studied via Hirshfeld surface (HS) analysis. Electrochemical performance tests reveal that 1 exhibits electrocatalytic activity toward the oxidation and reduction of diverse pollutants in water, including NO₂⁻, Cr(VI), BrO₃⁻, Fe(III), and ascorbic acid (AA). Additionally, it can also serve as an amperometric sensor for the detection of BrO₃⁻ and Cr(VI). Photocatalytic studies reveal that compound 1 functions as a bifunctional photocatalyst, which not only achieves efficient degradation of organic dyes but also demonstrates remarkable reduction efficiency for toxic Cr(VI). Compound 1 demonstrates significant potential for practical water remediation applications. Full article

With the advancement of industrialization and urbanization, the arbitrary emission of sewage containing TC-tetracycline and hexavalent chromium (Cr(VI)) possesses a serious threat to both ecological–environment and public health. However, developing a low-toxicity and cost-effective photocatalyst for the simultaneous elimination of these two pollutants remains a formidable task. This study devised a photocatalytic sample (CSMX-X) comprised of Copper(I) sulfide (Cu₂S) and Titanium carbide (Ti₃C₂) through a simple solvothermal method and applied it to remove TC-tetracycline and Cr(VI). The CSMX-X not only increases the specific surface area from 2.7 m²·g⁻¹ for pure Cu₂S to 30.65 m²·g⁻¹, but also effectively addresses the problems of insufficient separation efficiency of photogenerated holes and electrons and low carrier density. The photocatalytic efficiency for an individual pollutant (10 mg·L⁻¹ Cr(VI) or 20 mg·L⁻¹ TC-tetracycline) can reach more than 90%, while the removal efficiency for mixed Cr(VI) and TC-tetracycline pollutants only decreases by 12%. Meanwhile, copper leaching levels under different pH conditions (0.032–0.676 mg·L⁻¹) are considerably lower than the 2 mg·L⁻¹ safety standard set by the World Health Organization. This study provides valuable perspectives for constructing Cu₂S-based composite photocatalysts to remove multiple contaminants in real aquatic environments. Full article

Microplastics (MPs) and hexavalent chromium (Cr(VI)) are typical environmental pollutants, yet their interactions in aquatic systems remain poorly understood. This study investigates the mutual influence between Cr(VI) and both virgin and aged polystyrene microplastics (PS-MPs) under light conditions. Concentration kinetics revealed that the total chromium concentration remained stable across all systems, while Cr(VI) concentrations decreased over time, indicating that PS-MPs accelerate the reduction of Cr(VI) to Cr(III). Conversely, it had been found that Cr(VI) promoted the aging of PS-MPs, and this was evidenced by an increase in surface roughness and the generation of oxygen-containing functional groups. Cr(VI) led to a rise in the O/C ratio and carbonyl index, providing additional evidence for the aging of PS. Two-dimensional correlation spectroscopy (2D-COS) elucidated that under Cr(VI) exposure, the order of functional group alterations in PS and aged PS exhibited an opposite trend. Additionally, three-dimensional fluorescence spectroscopy revealed distinct changes in the fluorescence characteristics of leached substances from aged and pristine PS, both with and without Cr(VI), under light and dark conditions. These results furnish innovative understandings of environmental behavior and risks associated with the co-occurrence of MPs and heavy metals, highlighting the complex interplay between Cr(VI) and PS-MPs in aquatic environments. Full article

This study aimed to assess the long-term trends in PM₁₀, PM_2.5, and hazardous trace elements in Makkah from 2020 to 2024, evaluating seasonal variations, health risks, and potential mitigation strategies. The results indicated that the PM₁₀ concentrations ranged from a minimum of 127.7 ± 14.2 µg/m³ (2020) to a maximum of 138.3 ± 15.7 µg/m³ (2024), while PM_2.5 levels varied between 100.7 ± 18.7 µg/m³ and 109.8 ± 21.3 µg/m³. A seasonal analysis showed the highest PM₁₀ and PM_2.5 levels during winter (147.8 ± 16.4 µg/m³ and 119.5 ± 21.7 µg/m³ in 2024, respectively), coinciding with lower wind speeds and reduced dispersion. Among the nine trace elements analyzed, Cr VI exhibited the highest increase from 0.008 ± 0.001 µg/m³ (2020) to 0.012 ± 0.001 µg/m³ (2024), while Cd and Ni also rose significantly. The excess cancer risk (ECR) associated with these pollutants exceeded the recommended threshold, with a strong correlation between PM₁₀ and ECR (r = 0.85–0.93, p < 0.01). These findings highlight the need for enhanced air quality monitoring and sustainable urban planning. Future research should focus on identifying the dominant pollution sources and assessing the long-term health impacts to support evidence-based air quality management in Makkah. Full article

The rapid detoxification and mineralization of Cr(VI) in aqueous environments hold critical importance for emergency response and resource recovery yet remain technically challenging. Herein, we report the synthesis of FeS₂/ZVI composites through ethanol-assisted wet ball-milling and their application in Cr(VI) removal under microwave (MW) irradiation. This study systematically investigates the effects of MW irradiation on the removal efficiency of Cr(VI) using FeS₂/ZVI composites, with particular focus on key parameters including composite dosage, initial pH, MW temperature, and Cr(VI) concentration. Notably, 1 g/L FeS₂/ZVI composites achieved near-complete removal (>99%) of 50 mg/L Cr(VI) within 7 min at a MW irradiation temperature of 333 K, which exhibited 5.9-fold and 13.1-fold superior performance compared to pure pyrite and ZVI, respectively. Additionally, there is a 96.1% reduction in reaction time in comparison to non-MW irradiation system. In real electroplating wastewater samples, Cr(VI) concentration was reduced from 38.93 to 0.42 mg L⁻¹ by MW irradiation-assisted treatment, validating its potential for practical applications in industrial Cr(VI) pollution control. The activation energy determined by fitting the Arrhenius equation showed a 39.7% reduction for the MW-assisted FeS₂/ZVI system (16.0 kJ mol⁻¹) compared to conventional thermal heating (from 25.6 kJ mol⁻¹), indicating that MW irradiation induced catalytic enhancement of FeS₂/ZVI, thereby lowering the energy barrier for Cr(VI) reduction. Moreover, MW irradiation-assisted processes facilitated the mineralization of reduced Cr(III) to stable spinel FeCr₂O₄. These findings collectively establish a synergistic mechanism between MW activation and FeS₂/ZVI composites, offering innovative pathways for efficient Cr(VI) detoxification and resource recovery from high-strength industrial wastewaters. Full article